1. Field of the Invention
The present invention relates to radio-frequency identification (RFID) tag readers and a method of storing and remotely retrieving data from RFID tags or transponders.
2. Background Art
RFID tags or transponders are used to identify objects using radio waves. Generally, RFID tags contain an integrated circuit for storing and processing information, modulating and demodulating a radio-frequency signal and an antenna for receiving and transmitting the signal. One type of RFID tag is a passive RFID tag that has no internal power supply. The incoming radio-frequency signal from a reader provides power for the RFID tag to power-up and transmit a responsive signal. On the other hand, active RFID tags have their own power source that is used to power the integrated circuits of the active RFID tag to broadcast a signal to a reader.
RFID readers include a transmitter and receiver that are tuned to communicate with an RFID tag. RFID readers emit a signal that is received by the antenna of the RFID tag. The RFID tag responds to the signal from the RFID reader with a signal that includes a transmitted data packet. The transmitted data packet is decoded by the RFID reader and provided to a controller associated with the RFID reader.
RFID tags are sensitive to environmental factors that can alter the RF magnetic field. The proximity of an RFID tag to a metal object can distort the RF magnetic field making it difficult to establish communication between an RFID reader and an RFID tag. Even if an RFID tag is manufactured to communicate on a predetermined frequency, environmental interference may effectively change the radio-frequency signal. Load modulation is set on RFID readers by setting a manually tuneable capacitor generally between 40-100 pf. With current production RFID readers, once the load modulation is set in an RFID reader, it is not changed. The preset RFID reader may not work with all RFID tags due to changes in the RF magnetic field caused, in particular, in hostile environments or areas having metal objects that may cause interference. In addition, the resonant frequency of a group of RFID tags may vary from one to another rendering some RFID tags readable and others unreadable. The greater the difference between the frequency of the RFID tag and that of the RFID reader, the lower will be the strength and amount of modulation of the RFID tag output signal.
One application for RFID tags and RFID readers that has been developed is in the area of data storage. One example of such an RFID reader is provided on the T10000 tape drive manufactured by Sun Microsystems, Inc. that has a variable manual set capacitor manufactured by Panansonic. Data storage tape cartridges may be provided with an RFID tag that is placed in proximity to an RFID reader that forms part of a data storage tape drive. Data storage tape drives may have metallic components that can interfere with transmission and reception of the radio-frequency signals sent between the RFID tag and RFID reader. The RFID reader in a data storage tape drive is set during manufacture of the tape drive system to a selected frequency. When a data storage tape is placed in the drive, the reader of the data storage tape drive attempts to establish communication with the RFID tag. If the data signal is not received from the RFID tag, the RFID reader of the data storage tape drive may reject the tape cartridge. If a tape cartridge is rejected, replacement of the RFID tag or preparation of a substitute cartridge may be required.
These and other problems are addressed by Applicant's invention as summarized below.